Forget ammonia-based window cleaners! The windows in your home can be effectively cleaned with 4 tablespoons lemon juice mixed with a half gallon of water. Other effective cleaners for glass and mirrors are rubbing alcohol and witch hazel.
Another tip that old-fashioned household hint books often mention is that you can wipe windows clean with newspapers. While this may sound like a totally green idea -- after all, you'd be reusing newspapers and saving on paper towels -- the reality is that doing so is a messy and big waste of time. Try using a clean, lint-free rag instead, perhaps an old cotton T-shirt or cloth diaper.